Ecological footprint of farmed and caught salmon

Hon John van Dongen 17 July 2001
Minister of Agriculture, Food and Fisheries
Room #137
Parliament Buildings (Provincial Legislature)
Victoria, BC V6V 1X4

Dear Mr van Dongen:

Re: Moratorium on Net-Pen Salmon Farms
I am writing in response to the announcement that you are preparing to lift the moratorium on the construction of more net-pen salmon farms in British Columbia. My concern is rooted in the over-whelming evidence that net-pen rearing of salmon is an ecologically hazardous and economically questionable activity with that is fundamentally unsustainable.

You are no doubt aware of the multiple local ecological damage costs associated with net-pen rearing, from the local accumulation of nutrient and organic wastes, through the problem of disease transfers between farmed and wild stocks, to the issues raised by multiple large-scale escapes from farming operations. Such issues have triggered reassessments of the industry in Scotland and Norway of which your officials are no doubt aware. However, the main purpose of this letter is to inform you of other problems associated with the industry with which you may be unfamiliar.

Some years ago I pioneered a quantitative method to estimate the total ‘load’ imposed on ecosystems by any specified human population. This approach, called ‘ecological footprint analysis’ (EFA) has been further developed by my students and other scientists around the world and is increasingly used in assessing the sustainability of human society. EFA estimates the area of different ecosystem types required on a continuous basis to produce the resources consumed and to assimilate the wastes produced by a specified population (or economic activity). It can therefore be used to compare the ecological demands of a given population with, for example, that population’s domestic supply of ecologically productive lands. (It turns out that many high-income consumer countries live mainly on ‘imported’ carrying capacity.) It can also be used to assess the effect of different life-styles or alternative technologies on the sustainability of whole populations or economies.

Most recently we have been using a variation of the method as a form of ‘comparative technology assessment’ by which we compare the material and energy demands and ecosystem requirements of alternative production methods. One of my former PhD students, Peter Tyedmers, recently completed a multi-year comparative analysis of the net-pen salmon farming industry and the wild salmon fleet fishery. Some of the results of this study should be of particular interest to you and your officials in reconsidering the salmon farm moratorium.

To begin, farmed salmon are raised on feed pellets made 15% from slaughterhouse waste, 30% from grain crops, and 56% from rendered fish, including significant quantities of anchovy and jack mackerel from Peru and Chile. Dr Tyedmers found that the production of feed pellets consumes approximately 48,000 megajoules of mostly fossil energy per metric ton, including the energy to capture and process other lower-priced fish species. This is equivalent to1,300 litres of diesel fuel per metric ton of feed delivered to Campbell River, BC (in the vicinity of several fish farms). In the final analysis, the energy required to capture/process/transport the feed required to raise a live-weight kilogram of farmed Atlantic salmon is the equivalent of 2.4 litres of diesel fuel. Farmed chinook are even more energy intensive-about five litres diesel-fuel equivalent is required for feed to produce a kilogram of chinook fillets. (Keep in mind too that this is only part of the total energy story).

It should be no surprise, then, that the ecological footprints per tonne of product generated by salmon farms are considerably larger than those of the fleet fishery, regardless of species. Figure 1 compares the estimated total ecosystem demands of farmed Atlantic and chinook salmon with those of each of the five major salmonid species caught by the BC salmon fishing fleet. This figure hints at the fundamental unsustainability of salmon farming-the global ecological impact of salmon ‘farming’ is significantly greater than that of fishing, three-fold greater in the case of farmed chinook compared to caught pink salmon.

Ecological footprint graph
At least three additional points should be drawn from this study. First, net-pen salmon-farming is energetically similar to terrestrial forms of ‘factory’ livestock-raising in that far greater quantities of energy are expended in producing the ‘crop’ than is contained in the marketed product. Declining energy efficiency is an indicative property of both industrial agriculture and high-input mariculture. Before fossil fuel, farmers and their draught animals must have obtained at least marginally more energy from the harvest than they expended in cultivating the crop (otherwise they starved). By contrast, modern production agriculture produces less energy than it consumes and has an ever-declining output/input ratio. As a result, today’s food production systems embody more depletable fossil energy than ‘renewable’ solar energy. This ominous dependence is increasing even as stocks of cheap fossil fuel (particularly petroleum) are being depleted and global climate change threatens the stability of the entire process. On these grounds alone, society is moving ever further from sustainability in production agriculture and is foolishly repeating the process with high-input mariculture. [1]

Second, net-pen farms produce only one kg of salmon for every four or five kg of other fish (wet weight) embodied in feed pellets. Thus to produce 40,000 metric tons of salmon on BC salmon farms we must consume over 100,000 tons of other fish, mostly caught elsewhere. In short, salmon farming actually reduces global food supplies. Much of the southern hemisphere fish-catch destined for fish meal could be consumed directly by the poor in the exporting countries, rather than be used to produce a smaller quantity of salmon for rich consumers in the North. Surely there is a moral issue hidden in the money-driven global market for farm-raised salmon.

The third, and perhaps most important point in the long run, is that salmon farms are a costly and relatively inefficient technological substitute for a superior free service of nature. When salmon forage in the north Pacific they capture and concentrate into high quality protein the thinly dispersed energy fixed by marine photosynthesis over a vast and relatively unproductive (compared to inshore waters) region of ocean. It is beyond imagining that humans could develop a more efficient harvesting mechanism. To destroy wild salmon stocks through over-fishing, poor forest practices, other forms of habitat destruction, or climate change is not only morally reprehensible but deprives future generations forever of a great free gift of nature. As noted, the salmon farming industry expends large quantities of costly and increasingly scarce fossil fuel to do several jobs that wild salmon do for free, particularly foraging at sea to catch their food. This represents a waste of scarce financial and energy resources could be used for other socially productive purposes. [2]

To summarize, lifting the moratorium on net-pen salmon farms in response to pressures from the industry is not in the public interest. Salmon farms produce significant local ecological impacts that are well-documented here and elsewhere. Moreover, our own studies show that with its expanding ecological footprint, the salmon farming industry reduces the food available for human consumption (particularly in the developing world), contributes to global climate change through its considerable carbon dioxide emissions, and increases humanity’s food-dependence on depletable stocks of cheap fossil fuel. All in all, net-pen salmon farming is an ecologically and economically costly and therefore inherently unsustainable substitute for a service once provided free by nature.

I trust you will take these points into account before licensing more farming operations on the BC coast.


William E. Rees, PhD
c.c. Hon Joyce Murray, BC Minister of Water, etc.
Hon David Anderson, Environment Canada
Hon Herb Dhaliwal, Fisheries Canada


[1] Arguably, if fossil fuel prices were based on a full-social-cost accounting method, we couldn’t afford today’s net-pen salmon farms. (The ‘real’ social cost of of gasoline or diesel fuel is in the range of $2.00 to $6.00 per litre.)

[2] The fleet fishery also uses fossil fuel, but considerable less per kg of landed salmon than fish farms. The ideal capture method might well be a river-mouth trap fishery that takes returning spawners with little exogenous energy expenditure.


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